Mackerel has been overfished so much it is no longer a sustainable choice for a regular fish supper, conservationists have warned.

The Marine Conservation Society (MCS) said it had removed mackerel, an oily fish packed with omega 3, from its latest version of its "fish to eat" list, and should be eaten only occasionally.

The warning comes after the Marine Stewardship Council, which certifies fish stocks that are managed sustainably, suspended its certification of the north east Atlantic mackerel fishery.

Mackerel has long been seen as a cheaper and more sustainable alternative to other fish

Atlantic populations of mackerel have moved north west into Icelandic and Faroe Islands waters, prompting their fishermen to fish more stock than was previously agreed and causing a dispute between the countries that target the fishery.

Bernardette Clarke, fisheries officer at the MCS, said: "The stock has moved into Icelandic and Faroese waters, probably following their prey of small fish, crustaceans and squid.

"As a result, both countries have begun to fish more mackerel than was previously agreed.

"The total catch is now far in excess of what has been scientifically recommended and previously agreed upon by all participating countries. Negotiations to introduce new catch allowances have so far failed to reach agreement."

The conservation group said good alternatives to mackerel were herring and sardine, and if people wanted to continue to buy mackerel, they should ensure it is as sustainable as possible - for example, fish caught locally using traditional methods.

Another fish taken off the "fish to eat" list is gurnard, because of a lack of data on population levels and concerns about how stocks of the increasingly popular fish are being managed.

Because the fish has been historically caught accidentally as "bycatch" by fishing vessels targeting other species, there are no catch restrictions - but if stocks are being increasingly targeted, they need to be managed sustainably, the MCS said.

Many gurnard which are caught are discarded, a wasteful practice which sees useable fish thrown back into the sea, because there is still relatively low demand for them, Clarke added.

But the latest version of the "fish to eat" list shows that herring stocks, coley and Dover sole from the English Channel are all good to eat with a clear conscience.

Whiting from the Celtic Sea also appears on the list for the first time.

Cod stocks from the North Sea are still below recommended levels, the MCS said, but a number of other popular wild fish are given the green light to appear on the dinner plate, including haddock and lemon sole.

And farmed species are on the list, including organic Arctic charr, sturgeon caviar from closed fish farming systems, mussels, tiger prawns, Atlantic halibut and salmon and rainbow trout.

Clarke said: "As world population, fish consumption and reliance on fish imports from outside the European Union increases, the importance of knowing what we are eating, as well as where and how it is caught, is essential to allow consumers to make the most sustainable choice for the future of our fish."

The latest sustainable seafood advice from the Marine Conservation Society can be found by logging on to www.fishonline.org.

A spokesman for Defra said: "The continued sustainability of mackerel is vitally important and is increasingly threatened by the actions of the Faroe Islands and Iceland.

"We are extremely concerned that an agreement on fishing rights has not yet been reached.

"That is why the UK continues to seek a new agreement that is fair to all."